Boundary acoustic wave device

ABSTRACT

Regarding a boundary acoustic wave device in which at least a part of an IDT electrode is embedded in a groove disposed in a piezoelectric substrate, the acoustic velocity is increased. A boundary acoustic wave device is provided with a piezoelectric substrate, a first dielectric layer, and an IDT electrode. The surface of the piezoelectric substrate is provided with a groove. The IDT electrode is disposed at the boundary between the piezoelectric substrate and the first dielectric layer in such a way that at least a part thereof is located in the groove. In the inside of the groove, the groove angle γ, which is the size of an angle formed by an upper end portion of the inside surface of the groove with the surface of the piezoelectric substrate, is less than 90 degrees.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a boundary acoustic wave device for use as a resonator and a filter device, for example. In particular, the present invention relates to a boundary acoustic wave device in which at least a portion of an IDT electrode is embedded in a groove disposed in a piezoelectric substrate.

2. Description of the Related Art

The boundary acoustic wave device is an elastic wave device which does not require a package having a cavity and which can be miniaturized as compared with a surface acoustic wave device. Therefore, the boundary acoustic wave device has attracted rising attention in recent years.

For example, WO 2008/044411 A1 described below discloses a boundary acoustic wave device in which at least a portion of an IDT electrode is embedded in a groove disposed in a piezoelectric substrate. FIG. 78 is a magnified schematic cross-sectional view showing a portion of an IDT electrode of this boundary acoustic wave device. As shown in FIG. 78, a boundary acoustic wave device 101 is provided with a LiNbO₃ substrate 102. A silicon oxide film 103 is disposed on the LiNbO₃ substrate 102. An IDT electrode 104 is disposed at the boundary between the LiNbO₃ substrate 102 and the silicon oxide film 103. The IDT electrode 104 is embedded in a groove 102 a disposed in the LiNbO₃ substrate 102. The upper surface of the IDT electrode 104 must be flush with the surface of the LiNbO₃ substrate 102.

WO 2008/044411 A1 discloses that the upper surface of the IDT electrode 104 must be flush with the surface of the LiNbO₃ substrate 102, the upper surface of the silicon oxide film 103 is flat and, thereby, a low insertion loss can be realized.

However, regarding the boundary acoustic wave device 101 in which the IDT electrode 104 is embedded in the groove 102 a of the LiNbO₃ substrate 102, there is a problem in that the acoustic velocity of propagating boundary acoustic wave cannot be increased sufficiently.

SUMMARY OF THE INVENTION

In consideration of such circumstances, preferred embodiments of the present invention increase an acoustic velocity of a boundary acoustic wave device in which at least a portion of an IDT electrode is embedded in a groove disposed in a piezoelectric substrate.

A boundary acoustic wave device according to a preferred embodiment of the present invention includes a piezoelectric substrate, a first dielectric layer, and an IDT electrode. A surface of the piezoelectric substrate is provided with a groove. The first dielectric layer is disposed on the surface of the piezoelectric substrate. The IDT electrode is disposed at a boundary between the piezoelectric substrate and the first dielectric layer in such a way that at least a portion thereof is located in the groove. Inside of the groove, a groove angle, which is the size of an angle defined by an upper end portion of an inside surface of the groove with the surface of the piezoelectric substrate, is less than about 90 degrees, for example.

In the present specification, it is defined that the surface of the piezoelectric substrate does not include the bottom surface and the side surface of the groove.

In a preferred embodiment of the present invention, a portion of the IDT electrode is located outside the groove, and the portion of the IDT electrode located outside the groove is tapered so as to decrease in size moving away from the piezoelectric substrate. Regarding this configuration, it becomes difficult to form a gap between the first dielectric layer and the IDT electrode and, therefore, degradation in filter characteristic and resonant characteristic can be prevented.

In another preferred embodiment of the present invention, the boundary acoustic wave device is further provided with a second dielectric layer which is disposed on the first dielectric layer and which has an acoustic velocity larger than that of the first dielectric layer. A boundary acoustic wave is confined in the first dielectric layer effectively by disposing the second dielectric layer. Therefore, the insertion loss can be reduced because of a waveguide effect.

In another preferred embodiment of the present invention, each of the first and the second dielectric layers is preferably made of silicon oxide, silicon nitride, or aluminum nitride, for example.

In another preferred embodiment of the present invention, the average density of the portion of the IDT electrode located in the groove is higher than the average density of the piezoelectric substrate. In the case where the groove angle is less than about 90°, the stop band can be increased by specifying the average density of the portion, which is located in the groove, of the IDT electrode to be higher than the average density of the piezoelectric substrate.

In another preferred embodiment of the present invention, at least some portion of the portion of the IDT electrode located in the groove is made of at least one type of metal selected from the group consisting of Pt, Au, W, Ta, Mo, Ni, and Cu or an alloy containing at least one type of metal selected from the group consisting of Pt, Au, W, Ta, Mo, Ni, and Cu.

In another preferred embodiment of the present invention, the IDT electrode preferably includes a laminate of a plurality of electrode layers, and a resistivity of at least one layer of the plurality of electrode layers is about 5 μΩcm or less, for example. As a result, the insertion loss can be further reduced because the resistance of the IDT electrode can be reduced.

In another preferred embodiment of the present invention, the electrode layer having a resistivity of about 5 μΩcm or less is made of at least one type of metal selected from the group consisting of Al, Cu, Au, and Ag or an alloy containing at least one type of metal selected from the group consisting of Al, Cu, Au, and Ag.

In another preferred embodiment of the present invention, the IDT electrode preferably includes a laminate of a plurality of electrode layers, and a diffusion preventing film is disposed in at least one of a location between the IDT electrode and the bottom of the groove and a location between the electrode layers adjacent to each other. According to this configuration, diffusion of an electrode material between the electrode layers can be prevented. Furthermore, the adhesion between the electrode layers adjacent to each other can be enhanced.

In another preferred embodiment of the present invention, the diffusion preventing film is made of at least one type of metal selected from the group consisting of Ti, Ni, Cr, and Ta or an alloy containing at least one type of metal selected from the group consisting of Ti, Ni, Cr, and Ta.

In another preferred embodiment of the present invention, the piezoelectric substrate is made of LiTaO₃, for example.

In another preferred embodiment of the present invention, the IDT electrode includes a first electrode layer, which is located in the groove of the piezoelectric substrate and which contains Pt, and a second electrode layer, which is located outside the groove of the piezoelectric substrate and which contains Al, the first dielectric layer is made of silicon oxide, and θ of the Euler Angles (φ, θ, φ) and the groove angle γ are within the range specified in Tables 1 to 4 below and each of φ and φ of the Euler Angles is within the range of 0°±5°, where the Euler Angles of the piezoelectric substrate are specified to be (φ, θ, φ) and the groove angle is specified to be γ. According to this configuration, in the case where the piezoelectric substrate is made of LiTaO₃, the stop band can be further increased.

TABLE 1 Thickness of first θ of Euler Angles Thickness of first Thickness of second dielectric layer h/λ [%] (φ, θ, φ) [°] electrode layer h/λ [%] electrode layer h/λ [%] Groove angle [°] 10 < h < λ ≦ 30 124 < θ ≦ 128 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 37.1 ≦ γ < 90.0  7.5 < Al ≦ 12.5 39.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 39.5 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 37.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 32.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5 29.9 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 52.1 ≦ γ < 90.0  7.5 < Al ≦ 12.5 57.5 ≦ γ < 90.0 12.5 < Al ≦ 17.5 62.8 ≦ γ < 90.0 128 < θ ≦ 132 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 19.3 ≦ γ < 90.0  7.5 < Al ≦ 12.5 32.1 ≦ γ < 90.0 12.5 < Al ≦ 17.5 34.8 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 38.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5   34 ≦ γ < 90.0 12.5 < Al ≦ 17.5   30 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 49.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 50.3 ≦ γ < 90.0 12.5 < Al ≦ 17.5 50.8 ≦ γ < 90.0 132 < θ ≦ 136 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 18.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 27.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5   27 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5   40 ≦ γ < 90.0  7.5 < Al ≦ 12.5   35 ≦ γ < 90.0 12.5 < Al ≦ 17.5 32.7 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 49.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 39.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 47.4 ≦ γ < 90.0 136 < θ ≦ 140 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 18.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 32.5 ≦ γ < 90.0 12.5 < Al ≦ 17.5 37.3 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 41.3 ≦ γ < 90.0  7.5 < Al ≦ 12.5 38.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5   35 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 49.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 49.8 ≦ γ < 90.0 12.5 < Al ≦ 17.5 49.5 ≦ γ < 90.0

TABLE 2 Thickness of first θ of Euler Angles Thickness of first Thickness of second dielectric layer h/λ [%] (φ, θ, φ) [°] electrode layer h/λ [%] electrode layer h/λ [%] Groove angle [°] 10 < h < λ ≦ 30 140 < θ ≦ 144 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 41.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 46.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 46.3 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 46.6 ≦ γ < 90.0  7.5 < Al ≦ 12.5 41.7 ≦ γ < 90.0 12.5 < Al ≦ 17.5 38.1 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 51.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 39.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5   41 ≦ γ < 90.0 30 < h < λ ≦ 50 124 < θ ≦ 128 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 18.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 18.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 41.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 34.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 32.6 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 59.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 58.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5 33.0 ≦ γ < 90.0 128 < θ ≦ 132 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5   20 ≦ γ < 90.0  7.5 < Al ≦ 12.5 18.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 39.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 36.3 ≦ γ < 90.0 12.5 < Al ≦ 17.5 33.2 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 59.9 ≦ γ < 90.0  7.5 < Al ≦ 12.5 48.6 ≦ γ < 90.0 12.5 < Al ≦ 17.5 41.2 ≦ γ < 90.0 132 < θ ≦ 136 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 20.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 18.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 36.9 ≦ γ < 90.0  7.5 < Al ≦ 12.5 35.8 ≦ γ < 90.0 12.5 < Al ≦ 17.5 33.4 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 38.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 36.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 37.4 ≦ γ < 90.0

TABLE 3 Thickness of first θ of Euler Angles Thickness of first Thickness of second dielectric layer h/λ [%] (φ, θ, φ) [°] electrode layer h/λ [%] electrode layer h/λ [%] Groove angle [°] 30 < h < λ ≦ 50 136 < θ ≦ 140 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 22.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 19.3 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 40.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 30.7 ≦ γ < 90.0 12.5 < Al ≦ 17.5 32.3 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5   46 ≦ γ < 90.0  7.5 < Al ≦ 12.5   45 ≦ γ < 90.0 12.5 < Al ≦ 17.5 36.3 ≦ γ < 90.0 140 < θ ≦ 144 1 < Pt ≦ 3 2.5 < Al ≦ 7.5   19 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 26.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 22.7 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.1 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 41.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 39.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 40.7 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 46.9 ≦ γ < 90.0  7.5 < Al ≦ 12.5 46.1 ≦ γ < 90.0 12.5 < Al ≦ 17.5 45.7 ≦ γ < 90.0 50 < h < λ ≦ 70 124 < θ ≦ 128 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 56.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 46.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 36.5 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 33.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 29.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5 26.1 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 57.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 51.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 39.9 ≦ γ < 90.0 128 < θ ≦ 132 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 54.1 ≦ γ < 90.0  7.5 < Al ≦ 12.5 40.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 35.8 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 48.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 40.6 ≦ γ < 90.0 12.5 < Al ≦ 17.5 53.7 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 51.6 ≦ γ < 90.0  7.5 < Al ≦ 12.5 50.6 ≦ γ < 90.0 12.5 < Al ≦ 17.5   46 ≦ γ < 90.0

TABLE 4 Thickness of first θ of Euler Angles Thickness of first Thickness of second dielectric layer h/λ [%] (φ, θ, φ) [°] electrode layer h/λ [%] electrode layer h/λ [%] Groove angle [°] 50 < h < λ ≦ 70 132 < θ ≦ 136 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 18.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 42.6 ≦ γ < 90.0 12.5 < Al ≦ 17.5 27.6 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 34.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 32.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5   43 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 44.6 ≦ γ < 90.0  7.5 < Al ≦ 12.5 49.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 45.2 ≦ γ < 90.0 136 < θ ≦ 140 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 19.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 18.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 34.4 ≦ γ < 90.0  7.5 < Al ≦ 12.5   33 ≦ γ < 90.0 12.5 < Al ≦ 17.5 30.1 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 41.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5   48 ≦ γ < 90.0 12.5 < Al ≦ 17.5   44 ≦ γ < 90.0 140 < θ ≦ 144 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 26.3 ≦ γ < 90.0  7.5 < Al ≦ 12.5 19.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5   45 ≦ γ < 90.0  7.5 < Al ≦ 12.5 43.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 39.5 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 48.9 ≦ γ < 90.0  7.5 < Al ≦ 12.5 48.1 ≦ γ < 90.0 12.5 < Al ≦ 17.5   48 ≦ γ < 90.0

In another preferred embodiment of the present invention, the piezoelectric substrate is made of LiNbO₃, for example.

In another preferred embodiment of the present invention, the following relationships −5°≦φ≦+5°, +80°≦θ≦+130°, −10°≦φ≦+10°, and 10°≦γ<90° are satisfied, where the Euler Angles of the piezoelectric substrate are specified to be (φ, θ, φ) and the groove angle is specified to be γ. Regarding this configuration, in the case where the piezoelectric substrate is made of LiNbO₃ and a boundary acoustic wave in a SH (Shear Horizontal) mode is utilized, the stop band can be further increased.

In another preferred embodiment of the present invention, the following relationshiops −5°≦φ≦+5°, +200°≦θ≦+250°, −10°≦φ≦+10°, and 10°≦γ<90° are satisfied, where the Euler Angles of the piezoelectric substrate are specified to be (φ, θ, φ) and the groove angle is specified to be γ. Regarding this configuration, in the case where the piezoelectric substrate is made of LiNbO₃ and a boundary acoustic wave in a Stoneley mode is utilized, the stop band can be further increased.

In another preferred embodiment of the present invention, the groove angle is preferably within the range of about 10° or more and about 80° or less. Regarding this configuration, the acoustic velocity can be further increased.

According to various preferred embodiments of the present invention, a boundary acoustic wave device including a piezoelectric substrate, a first dielectric layer disposed on the piezoelectric substrate, and an IDT electrode disposed at a boundary between the piezoelectric substrate and the first dielectric layer, a groove angle of a groove in the piezoelectric substrate, in which at least a portion of the IDT electrode is embedded, is preferably less than about 90 degrees and, thereby, the acoustic velocity can be further increased.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a boundary acoustic wave device according to a preferred embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a boundary acoustic wave device.

FIG. 3 is a graph showing the relationship between the groove angle γ and the acoustic velocity of a boundary acoustic wave in the case where an IDT electrode is made of Al.

FIG. 4 is a graph showing the relationship between the groove angle γ and the acoustic velocity of a boundary acoustic wave in the case where an IDT electrode is made of Pt.

FIG. 5 is a graph showing the relationship between the groove angle γ and the stop band in the case where an IDT electrode is made of Al.

FIG. 6 is a graph showing the relationship between the groove angle γ and the stop band in the case where an IDT electrode is made of Pt.

FIG. 7 is a magnified schematic cross-sectional view of a portion of an IDT electrode in a first modified preferred embodiment of the present invention.

FIG. 8 is a graph showing the relationship between the groove angle γ and the stop band, where the film thickness of a first electrode layer normalized by the wave length is about 1%, the film thickness of a portion, which is located in a groove 10 a, of a second electrode layer normalized by the wave length is about 5%, and the film thickness of a portion, which is located outside the groove 10 a, of the second electrode layer normalized by the wave length is about 10%.

FIG. 9 is a graph showing the relationship between the groove angle γ and the stop band, where the film thickness of a first electrode layer normalized by the wave length is about 3%, the film thickness of a portion, which is located in a groove 10 a, of a second electrode layer normalized by the wave length is about 3%, and the film thickness of a portion, which is located outside the groove 10 a, of the second electrode layer normalized by the wave length is about 10%.

FIG. 10 is a graph showing the relationship between the groove angle γ and the stop band, where the film thickness of a first electrode layer normalized by the wave length is about 5%, the film thickness of a portion, which is located in a groove 10 a, of a second electrode layer normalized by the wave length is about 1%, and the film thickness of a portion, which is located outside the groove 10 a, of the second electrode layer normalized by the wave length is about 10%.

FIG. 11 is a magnified schematic cross-sectional view of a portion of an IDT electrode in a second modified preferred embodiment of the present invention.

FIG. 12 is a magnified schematic cross-sectional view of a portion of an IDT electrode in a third modified preferred embodiment of the present invention.

FIG. 13 is a magnified schematic cross-sectional view of a portion of an IDT electrode in a fourth modified preferred embodiment of the present invention.

FIG. 14 is a magnified schematic cross-sectional view of a portion of an IDT electrode in a fifth modified preferred embodiment of the present invention.

FIG. 15 is a magnified schematic cross-sectional view of a portion of an IDT electrode in a sixth modified preferred embodiment of the present invention.

FIG. 16 is a magnified schematic cross-sectional view of a portion of an IDT electrode in a seventh modified preferred embodiment of the present invention.

FIG. 17 is a magnified schematic cross-sectional view of a portion of an IDT electrode in an eighth modified preferred embodiment of the present invention.

FIG. 18 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 126°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 19 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 126°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 20 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 126°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 21 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 126°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 22 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 130°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 23 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 130°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 24 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 130°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 25 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 130°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 26 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 134°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 27 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 134°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 28 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 134°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 29 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 134°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 30 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 138°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 31 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 138°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 32 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 138°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 33 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 138°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 34 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 142°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 35 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 142°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 36 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 142°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 37 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 142°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 20%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 38 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 126°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 39 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 126°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 40 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment, where a LiTaO₃ substrate having Euler Angles of)(0°, 126°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 41 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 126°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 42 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 130°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 43 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 130°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 44 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 130°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 45 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 130°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 46 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 134°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 47 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 134°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 48 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 134°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 49 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 134°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 50 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 138°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 51 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment, where a LiTaO₃ substrate having Euler Angles of)(0°, 138°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 52 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO3 substrate having Euler Angles of)(0°, 138°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO2 normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 53 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 138°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 54 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 142°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 55 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 142°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 56 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 142°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 57 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 142°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 40%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 58 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 126°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 59 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 126°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 60 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 126°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 61 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°,126°,0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 62 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 130°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 63 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 130°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 64 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 130°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 65 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 130°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 66 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 134°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 67 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment, where a LiTaO₃ substrate having Euler Angles of)(0°, 134°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is 4%, the film thickness of Al normalized by the wave length is 5%, 10%, or 15%, the film thickness of SiO₂ normalized by the wave length is 60%, the film thickness of SiN normalized by the wave length is 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 68 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 134°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 69 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 134°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 70 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 138°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 71 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 138°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 72 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 138°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 73 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 138°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 74 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment, where a LiTaO₃ substrate having Euler Angles of)(0°, 142°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 2%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 75 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 142°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 4%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 76 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 142°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 6%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 77 is a graph showing the relationship between the groove angle γ and the stop band in the eighth modified preferred embodiment of the present invention, where a LiTaO₃ substrate having Euler Angles of)(0°, 142°, 0°) is used as the piezoelectric substrate, the film thickness of Pt normalized by the wave length is about 8%, the film thickness of Al normalized by the wave length is about 5%, about 10%, or about 15%, the film thickness of SiO₂ normalized by the wave length is about 60%, the film thickness of SiN normalized by the wave length is about 100%, and the film thickness of Ti between the individual layers normalized by the wave length is about 10%.

FIG. 78 is a magnified schematic cross-sectional view of a portion of an IDT electrode of a boundary acoustic wave device described in WO 2008/044411 A1.

FIG. 79 is a magnified schematic cross-sectional view of a portion of an IDT electrode in a ninth modified preferred embodiment of the present invention.

FIG. 80 shows the relationship between the groove angle (γ) and the stop band, where the cross-sectional shape is as shown in FIG. 17 and the piezoelectric substrate is formed from a LiNbO₃ substrate having Euler Angles of (0,85°, 0).

FIG. 81 shows the relationship between the groove angle (γ) and the stop band, where the cross-sectional shape is as shown in FIG. 17 and the piezoelectric substrate is formed from a LiNbO₃ substrate having Euler Angles of (0,95°, 0).

FIG. 82 shows the relationship between the groove angle (γ) and the stop band, where the cross-sectional shape is as shown in FIG. 17 and the piezoelectric substrate is formed from a LiNbO₃ substrate having Euler Angles of (0, 105°, 0).

FIG. 83 shows the relationship between the groove angle (γ) and the stop band, where the cross-sectional shape is as shown in FIG. 17 and the piezoelectric substrate is formed from a LiNbO₃ substrate having Euler Angles of (0, 115°, 0).

FIG. 84 shows the relationship between the groove angle (γ) and the stop band, where the cross-sectional shape is as shown in FIG. 17 and the piezoelectric substrate is formed from a LiNbO₃ substrate having Euler Angles of (0, 125°, 0).

FIG. 85 shows the relationship between the groove angle (γ) and the stop band, where the cross-sectional shape is as shown in FIG. 17 and the piezoelectric substrate is formed from a LiNbO₃ substrate having Euler Angles of (0, 205°, 0).

FIG. 86 shows the relationship between the groove angle (γ) and the stop band, where the cross-sectional shape is as shown in FIG. 17 and the piezoelectric substrate is formed from a LiNbO₃ substrate having Euler Angles of (0, 215°, 0).

FIG. 87 shows the relationship between the groove angle (γ) and the stop band, where the cross-sectional shape is as shown in FIG. 17 and the piezoelectric substrate is formed from a LiNbO₃ substrate having Euler Angles of (0, 225°, 0).

FIG. 88 shows the relationship between the groove angle (γ) and the stop band, where the cross-sectional shape is as shown in FIG. 17 and the piezoelectric substrate is formed from a LiNbO₃ substrate having Euler Angles of (0, 235°, 0).

FIG. 89 shows the relationship between the groove angle (γ) and the stop band, where the cross-sectional shape is as shown in FIG. 17 and the piezoelectric substrate is formed from a LiNbO₃ substrate having Euler Angles of (0, 245°, 0).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be made clear by explaining preferred embodiments below with reference to drawings.

FIG. 1 is a schematic plan view of a boundary acoustic wave device according to the present preferred embodiment. FIG. 2 is a schematic cross-sectional view of the boundary acoustic wave device according to the present preferred embodiment. As shown in FIG. 2, a boundary acoustic wave device 1 preferably is a so-called three-media boundary acoustic wave device and is provided with a piezoelectric substrate 10 and first and second dielectric layers 11 and 12.

The piezoelectric substrate 10 is not specifically limited insofar as it is formed from a piezoelectric material. The piezoelectric substrate 10 can be made of, for example, a LiNbO₃ substrate or a LiTaO₃ substrate.

A first dielectric layer 11 is disposed on the piezoelectric substrate 10. A second dielectric layer 12 is disposed on the first dielectric layer 11. The acoustic velocity of the second dielectric layer 12 is larger than the acoustic velocity of the first dielectric layer 11.

The materials for the first and second dielectric layers 11 and 12 are not specifically limited insofar as the acoustic velocity of the second dielectric layer 12 is larger than the acoustic velocity of the first dielectric layer 11. For example, the first and second dielectric layers 11 and 12 can be made of aluminum nitride, e.g., AlN, besides silicon oxides, e.g., SiO₂, silicon nitrides, e.g., SiN, and the like.

More specifically, for example, the first dielectric layer 11 can be made of silicon oxides, e.g., SiO₂, and the second dielectric layer 12 can be made of a silicon nitride, e.g., SiN, or an aluminum nitride, e.g., AlN.

An IDT electrode 13 is disposed at the boundary between the piezoelectric substrate 10 and the first dielectric layer 11. At least a portion of the IDT electrodes 13 are located in a plurality of grooves 10 a disposed in the piezoelectric substrate 10. That is, at least a portion of the IDT electrodes 13 are embedded in a plurality of grooves 10 a disposed in the piezoelectric substrate 10. Specifically, in the present preferred embodiment, the whole IDT electrode 13 is embedded in the groove 10 a. The surface of the IDT electrode 13 is preferably flush with the surface 10 b of the piezoelectric substrate 10.

As shown in FIG. 1, in the present preferred embodiment, the IDT electrode 13 includes first to third IDT electrodes 13A, 13B, and 13C, each preferably defined by a pair of comb-shaped electrodes which are interdigitated with each other. The first to the third IDT electrodes 13A, 13B, and 13C are arranged along the propagation direction of the boundary acoustic wave. Grating reflectors 14 and 15 are disposed on both sides of the first to the third IDT electrodes 13A, 13B, and 13C in the propagation direction of the boundary acoustic wave. These grating reflectors 14 and 15 are also embedded in the groove 10 a disposed in the piezoelectric substrate 10.

As shown in FIG. 2, the cross-sectional shape of the groove 10 a, in which the IDT electrode 13 is embedded, is specified to be a shape having a width which decreases with decreasing away from the surface 10 b of the piezoelectric substrate 10. In the present preferred embodiment, the cross-sectional shape of the groove 10 a is preferably nearly trapezoidal. In this regard, among the angles formed by an upper end portion, which is located on the surface 10 b side of the piezoelectric substrate 10, of the inside surface of the groove 10 a with the surface 10 b of the piezoelectric substrate 10, the size of an angle (groove angle) γ located on the side inside the groove 10 a is specified to be less than about 90 degrees, for example. Consequently, the acoustic velocity of the boundary acoustic wave generated in the IDT electrode 13 is increased, as described below.

FIG. 3 is a graph showing the relationship between the groove angle γ and the acoustic velocity of a boundary acoustic wave in the case where the IDT electrode 13 is made of Al. As is clear from the results shown in FIG. 3, the acoustic velocity of the boundary acoustic wave can be increased as compared with that in the case where the groove angle is about 90° by setting the groove angle γ to be less than about 90°. Furthermore, it is clear that in the case where the IDT electrode 13 disposed in the groove 10 a is made of Al having a low density, the acoustic velocity of the boundary acoustic wave increases linear functionally as the groove angle γ decreases.

FIG. 4 is a graph showing the relationship between the groove angle γ and the acoustic velocity of a boundary acoustic wave in the case where the IDT electrode γ is preferably made of Pt. As is clear from the results shown in FIG. 4, in the case where the IDT electrode γ is made of Pt as well, the acoustic velocity of the boundary acoustic wave can also be increased as compared with that in the case where the groove angle is about 90° by setting the groove angle γ to be less than about 90°. However, it is clear that in the case where the IDT electrode 13 disposed in the groove 10 a is made of Pt having a high density, the rate of change in acoustic velocity of the boundary acoustic wave relative to a decrease in groove angle γ tends to increase as the groove angle γ decreases. If the groove angle γ is larger than about 80°, the acoustic velocity of the boundary acoustic wave does not increase significantly as the groove angle γ decreases. On the other hand, if the groove angle γ is about 80° or less, the acoustic velocity of the boundary acoustic wave increases significantly as the groove angle γ decreases.

From these results, the acoustic velocity of the boundary acoustic wave can be increased as compared with that in the case where the groove angle γ is about 90° by setting the groove angle γ to be less than about 90° regardless of the type of the IDT electrode 13. In this regard, it is preferable that the groove angle γ is about 80° or less, for example. The acoustic velocity of the boundary acoustic wave can be increased significantly regardless of the type of the IDT electrode 13 by setting the groove angle γ to be about 80° or less.

The lower limit of the groove angle γ is not specifically limited with respect to the relationship with the acoustic velocity of the boundary acoustic wave. However, the lower limit of the groove angle γ is, for example, preferably about 10°, preferably about 30°, preferably about 45°, and more preferably about 55°.

The design parameters of the boundary acoustic wave devices which exhibit the acoustic velocities of the boundary acoustic wave shown in FIGS. 3 and 4 are as described below.

Piezoelectric substrate 10: LiTaO₃ substrate having rotation angles of (0, 138°, 0)

Electrode finger ratio (duty) of IDT electrode 13: 0.5

First dielectric layer 11: SiO₂ layer (film thickness normalized by wave length: 40%)

Second dielectric layer 12: SiN layer (film thickness normalized by wave length: 100%)

Next, regarding the case shown in FIG. 3 where the IDT electrode 13 is made of Al, the relationship between the groove angle and the stop band will be described. The results thereof are shown in FIG. 5. Likewise, regarding the case shown in FIG. 4 where the IDT electrode 13 is made of Pt, the relationship between the groove angle and the stop band will be described. The results thereof are shown in FIG. 6.

As shown in FIG. 5, in the case where the IDT electrode 13 is made of Al having a low density, the stop band tends to become small as the groove angle γ becomes small. In the case where the IDT electrode 13 is made of Al having a low density, the stop band tends to linear functionally become small as the groove angle γ becomes small.

On the other hand, in the case where the IDT electrode 13 is made of Pt having a high density and the groove angle is less than about 90°, the stop band tends to become larger than that in the case where the groove angle γ is about 90°.

As is clear from these results, the stop band can be increased while the acoustic velocity of the boundary acoustic wave is increased by specifying the groove angle γ to be less than about 90° and, in addition, forming the IDT electrode 13 of a high-density, electrically conductive material, e.g., Pt.

In this regard, as is clear from the results shown in FIG. 6, in the case where the IDT electrode 13 is made of Pt having a high density, the acoustic velocity of the boundary acoustic wave does not linear functionally increase as the groove angle γ decreases. In the range of the groove angle γ of about 90° to about 70°, the stop band tends to increase monotonously as the groove angle γ decreases, although in the range of the groove angle γ less than about 70°, the stop band tends to decrease monotonously as the groove angle γ decreases. However, even in the case where the groove angle γ is about 55°, the stop band is larger than that in the case where the groove angle γ is about 90°. Therefore, it is clear that in the case where the IDT electrode 13 is made of Pt, in order to increase the stop band, the groove angle γ is preferably less than about 90° and about 55° or more, and further preferably about 70°.

Next, the relationship between the electrode density of the IDT electrode 13 and the stop band was determined. In each of the case where the groove angle γ is about 60° and the case where the groove angle γ is about 90°, when the average density of the IDT electrode 13 is changed variously, the relationship with the size of the stop band is shown in Table 5 described below.

TABLE 5 Density of IDT electrode 13 Stop band (g/cm³) Groove angle γ = 60° Groove angle γ = 90° 2.69 1.873 1.960 4.54 1.500 1.735 8.93 0.444 0.360 16.6 6.278 6.217 21.37 10.411 10.368

As shown in Table 5 described above, in the case where the average density of the IDT electrode 13 is smaller than the density (about 7.45 g/cm³) of the piezoelectric substrate 10 (LiTaO₃ substrate), the stop band in the case where the groove angle γ was about 90° was larger than that in the case where the groove angle γ was about 60°. On the other hand, in the case where the average density of the IDT electrode 13 is larger than the density (about 7.45 g/cm³) of the piezoelectric substrate 10, the stop band in the case where the groove angle γ was about 60° was larger than that in the case where the groove angle γ was about 90°. As is clear from these results, in the case where the IDT electrode 13 is embedded in the groove 10 a completely and the surface of the IDT electrode 13 is flush with the surface 10 b of the piezoelectric substrate 10, the effect that the stop band is increased by reducing the groove angle γ is obtained when the average density of the IDT electrode 13 is larger than the average density of the piezoelectric substrate 10. That is, it is clear that the stop band can be increased while the acoustic velocity of the boundary acoustic wave is increased by making the average density of the IDT electrode 13 larger than the average density of the piezoelectric substrate 10 and, in addition, specifying the groove angle γ to be less than about 90°.

Therefore, the material for the IDT electrode 13 located in the groove 10 a is not specifically limited insofar as the material is an electrically conductive material. However, it is preferable that at least a portion of the IDT electrode 13 is made of a high-density, electrically conductive material, e.g., one type of metal selected from the group consisting of Pt, Au, W, Ta, Mo, Ni, and Cu or an alloy containing at least one type of metal selected from the group consisting of Pt, Au, W, Ta, Mo, Ni, and Cu.

The modified preferred embodiments of the above-described preferred embodiments will be described below. In this regard, in the following explanations, members having substantially the same functions as the members in the above-described first preferred embodiment will be indicated by the same reference numerals as those set forth above and explanations thereof will be omitted.

First Modified Preferred Embodiment

In the above-described first preferred embodiment, the example in which the whole IDT electrode 13 is embedded in the groove 10 a and the IDT electrode 13 includes a single electrically conductive layer, is explained. However, the present invention is not limited to this configuration. For example, only a portion of the IDT electrode 13 may be embedded in the groove 10 a and the other portion may be located on the side upper than the surface 10 b of the piezoelectric substrate 10. Furthermore, the IDT electrode 13 may include a laminate of a plurality of electrically conductive layers.

In the present modified preferred embodiment, as shown in FIG. 7, the IDT electrode 13 preferably includes an electrode layer laminate of a first electrode layer 13 a, which is disposed on the piezoelectric substrate 10 in such a way that at least a portion thereof is located in the groove 10 a, and a second electrode layer 13 b, which is laminated on the first electrode layer 13 a. A portion of the IDT electrode 13 is located on the side upper than the surface 10 b of the piezoelectric substrate 10. More specifically, the first electrode layer 13 a is disposed in the groove 10 a. Then, a portion of the second electrode layer 13 b is located in the groove 10 a, and the remainder portion is located on the side upper than the surface 10 b of the piezoelectric substrate 10.

Alternatively, as shown in FIG. 79, a portion 13Y, which is located outside the groove 10 a, of the IDT electrode 13 may taper with decreasing distance away from the piezoelectric substrate 10. In the example shown in FIG. 79, the cross-sectional shape of the portion 13Y, which is located outside the groove 10 a, of the IDT electrode 13 preferably has a nearly trapezoidal shape in which the length T of the upper base is smaller than the length R of the lower base.

As shown in FIG. 79, the portion 13Y, which is located outside the groove 10 a, of the IDT electrode 13 is specified to have a tapered shape and, thereby, a gap is not formed easily between the first dielectric layer 11 and the IDT electrode 13. Therefore, scattering of a boundary acoustic wave due to formation of a gap between the first dielectric layer 11 and the IDT electrode 13 can be suppressed. As a result, degradation in characteristics, e.g., an insertion loss, can be suppressed.

Meanwhile, in the case where the first dielectric layer 11 is made of silicon oxide, degradation in temperature characteristics of frequency due to formation of a gap between the first dielectric layer 11 and the IDT electrode 13 can also be suppressed.

In this regard, the cross-sectional shape of the portion 13Y, which is located outside the groove 10 a, of the IDT electrode 13 is not limited to the nearly trapezoidal shape and may be a semi-elliptic shape, a semi-oval shape, a triangular shape, or the like.

The first electrode layer 13 a is made of a material, e.g., at least one type of metal selected from the group consisting of Pt, Au, W, Ta, Mo, Ni, and Cu or an alloy containing at least one type of metal selected from the group consisting of Pt, Au, W, Ta, Mo, Ni, and Cu, having a density higher than the piezoelectric substrate 10. Furthermore, the average density of a portion 13Z, which is located in the groove 10 a, of the IDT electrode 13 is specified to become higher than the average density of the piezoelectric substrate 10. That is, the average density of the first electrode layer 13 a and the portion, which is located in the groove 10 a, of the second electrode layer 13 b is specified to become higher than the average density of the piezoelectric substrate 10. Concretely, in the present preferred embodiment, the first electrode layer is made of Pt, and the second electrode layer is made of Al.

Table 6 described below shows the average density of the portion 13Z, which is located in the groove 10 a, of the IDT electrode 13, where the ratio of the thickness of the first electrode layer 13 a to the thickness of the portion, which is located in the groove 10 a, of the second electrode layer 13 b is changed variously.

Moreover, FIG. 8 shows the relationship between the groove angle γ and the stop band, where the film thickness of the first electrode layer 13 a normalized by the wave length is 1%, the film thickness of the portion, which is located in the groove 10 a, of the second electrode layer 13 b normalized by the wave length is 5%, and the film thickness of the portion, which is located outside the groove 10 a, of the second electrode layer 13 b normalized by the wave length is 10%.

FIG. 9 shows the relationship between the groove angle γ and the stop band, where the film thickness of the first electrode layer 13 a normalized by the wave length is 3%, the film thickness of the portion, which is located in the groove 10 a, of the second electrode layer 13 b normalized by the wave length is 3%, and the film thickness of the portion, which is located outside the groove 10 a, of the second electrode layer 13 b normalized by the wave length is 10%.

FIG. 10 shows the relationship between the groove angle γ and the stop band, where the film thickness of the first electrode layer 13 a normalized by the wave length is 5%, the film thickness of the portion, which is located in the groove 10 a, of the second electrode layer 13 b normalized by the wave length is 1%, and the film thickness of the portion, which is located outside the groove 10 a, of the second electrode layer 13 b normalized by the wave length is 10%.

In this regard, in FIG. 8 to FIG. 10, the graph indicated by “134°” is the graph in the case where the LiTaO3 substrate having rotation angles of)(0°, 134°, 0°) is used as the piezoelectric substrate 10. The graph indicated by “138°” is the graph in the case where the LiTaO3 substrate having rotation angles of)(0°, 138°, 0°) is used as the piezoelectric substrate 10. The graph indicated by “142°” is the graph in the case where the LiTaO3 substrate having rotation angles of)(0°, 142°, 0°) is used as the piezoelectric substrate 10.

TABLE 6 First Portion, which is located Average electrode in groove 10a, of second density layer 13a electrode layer 13b (g/cm³) Density (g/cm³) 21.5 2.7 Thickness (%) 1 5 5.41 2 4 8.29 3 3 11.34 4 2 14.56 5 1 17.95

As shown in Table 6 described above, in the case where the film thickness of the first electrode layer 13 a normalized by the wave length is 1% and the film thickness of the portion, which is located in the groove 10 a, of the second electrode layer 13 b normalized by the wave length is 5%, the average density of the portion, which is located in the groove 10 a, of the IDT electrode 13 is 5.41 g/cm³ and is smaller than the density (7.45 g/cm³) of the piezoelectric substrate 10 (LiTaO₃ substrate). In this case, as shown in FIG. 8, the stop band is the largest when the groove angle γ is 90°, and the stop band tends to become small as the groove angle γ becomes small from 90°.

As shown in Table 6 described above, in the case where the film thickness of the first electrode layer 13 a normalized by the wave length is 3% and the film thickness of the portion, which is located in the groove 10 a, of the second electrode layer 13 b normalized by the wave length is 3%, the average density of the portion, which is located in the groove 10 a, of the IDT electrode 13 is 11.34 g/cm³ and is larger than the density (7.45 g/cm³) of the piezoelectric substrate 10 (LiTaO₃ substrate). Likewise, in the case where the film thickness of the first electrode layer 13 a normalized by the wave length is 5% and the film thickness of the portion, which is located in the groove 10 a, of the second electrode layer 13 b normalized by the wave length is 1%, the average density of the portion, which is located in the groove 10 a, of the IDT electrode 13 is 17.95 g/cm³ and is larger than the density (7.45 g/cm³) of the piezoelectric substrate 10 (LiTaO₃ substrate). In these cases, as shown in FIG. 9 and FIG. 10, it is clear that the stop band can be made larger than the stop band in the case where the groove angle γ is specified to be 90° by specifying the groove angle γ to be less than 90°.

As is clear from these results, in the case where the IDT electrode 13 is formed from the electrically conductive layer laminate as well, the stop band can be increased while the acoustic velocity of the boundary acoustic wave is increased by making the average density of the portion 13Z, which is located in the groove 10 a, of the IDT electrode 13 larger than the average density of the piezoelectric substrate 10. Furthermore, as is also clear, the effect that the stop band can be increased while the acoustic velocity of the boundary acoustic wave is increased by making the average density of the portion 13Z, which is located in the groove 10 a, of the IDT electrode 13 larger than the average density of the piezoelectric substrate 10 is obtained likewise in the case where only a part of the IDT electrode 13 is located in the groove 10 a and the other portion is located on the side upper than the surface 10 b of the piezoelectric substrate 10.

In this regard, the material for the second electrode layer 13 b is not specifically limited insofar as the material is an electrically conductive material. The material for the second electrode layer 13 b may have a density higher than the density of the piezoelectric substrate 10 or be lower than that. For example, the second electrode layer 13 b may be made of a material, e.g., at least one type of metal selected from the group consisting of Al, Ag, Pt, Au, W, Ta, Mo, Ni, and Cu or an alloy containing at least one type of metal selected from the group consisting of Al, Ag, Pt, Au, W, Ta, Mo, Ni, and Cu, having a density higher than that of the piezoelectric substrate 10.

However, if the electrical resistivity of the IDT electrode 13 increases, the insertion loss of the boundary acoustic wave device becomes large. Therefore, it is preferable that the second electrode layer 13 b is made of a metal or an alloy having a low electrical resistivity. The electrical resistivity of the second electrode layer 13 b is preferably 5 μΩcm or less. Consequently, it is preferable that the second electrode layer 13 b is made of a low-resistivity material, e.g., at least one type of metal selected from the group consisting of Al, Cu, Au, and Ag or an alloy containing at least one type of metal selected from the group consisting of Al, Cu, Au, and Ag.

Next, regarding the structure having a cross-sectional shape shown in FIG. 17, the relationships among θ of the Euler Angles (φ, θ, φ) of the piezoelectric substrate 10, the groove angle γ, and the stop band were examined, where the piezoelectric substrate 10 was made of LiTaO₃.

As shown in FIG. 17, regarding the boundary acoustic wave device produced in the present experiment, the IDT electrode 13 was formed from a laminate in which a first diffusion preventing film 13 c, a first electrode layer 13 a, a second diffusion preventing film 13 d, a second electrode layer 13 b, and a third diffusion preventing film 13 e were laminated in that order from the piezoelectric substrate 10 side. Each of the first to the third diffusion preventing films 13 c to 13 e was made of a Ti film having a film thickness normalized by the wave length of 0.5%. The first electrode layer 13 a was made of a Pt film having a film thickness normalized by the wave length of 2%, 4%, 6%, or 8%. The second electrode layer 13 b was made of an Al film having a film thickness normalized by the wave length of 5%, 10%, or 15%. In this regard, the first diffusion preventing film 13 c and the first electrode layer 13 a were located in the groove 10 a, and the other portions were located outside the groove 10 a. The first dielectric layer 11 was made of a SiO₂ film having a film thickness normalized by the wave length of 20%, 40%, or 60%, and the second dielectric film 12 was made of a SiN film having a film thickness normalized by the wave length of 100%.

FIG. 18 to FIG. 77 show the relationship between the groove angle γ and the stop band, where the piezoelectric substrate was made of a LiTaO₃ substrate having Euler Angles of (0°, 126° to 142°, 0°), the film thickness of Pt normalized by the wave length was 2%, 4%, 6%, or 8%, the film thickness of Al normalized by the wave length was 5%, 10%, or 15%, and the film thickness of SiO₂ normalized by the wave length was 20%, 40%, or 60%.

Moreover, approximate expressions of the data under the individual conditions shown in FIG. 18 to FIG. 77 were calculated by using the method of least squares. In this regard, the approximate expression was assumed to be a quadratic function (y=ax²±bx+c, where y represents a stop band and x represents a groove angle). The values of a, b, and c in the calculated approximate expressions of the data under the individual conditions are shown in Tables 7 to 11 described below.

Furthermore, on the basis of the resulting approximate expression, the size of a stop band when the groove angle was 90° and the lower limit value of the groove angle of the region in which the stop band was larger than or equal to the stop band when the groove angle was 90°, that is, the groove angle at which the stop band was equal to the stop band when the groove angle was 90° was calculated. The results thereof are also shown in Table 7 to Table 11 described below.

TABLE 7 Thickness Thickness Thickness Lower limit value of groove of first of first of second Stop band angle of region in which Cut dielectric electrode electrode when stop band is larger than or angle layer h/λ layer h/λ layer h/λ groove equal to stop band when (θ) [%] [%] [%] a b c angle = 90° groove angle = 90° (°) 126 20 2 5 −5.014E−05 4.610E−03 3.538 3.547 1.942 126 40 2 5 −3.973E−05 2.005E−03 4.270 4.129 −39.524 126 60 2 5 −2.388E−05 −5.770E−04 4.291 4.045 −114.163 126 20 2 10 −3.853E−05 2.947E−03 3.700 3.653 −13.523 126 40 2 10 −3.131E−05 4.957E−04 4.439 4.230 −74.166 126 60 2 10 −2.209E−05 −1.011E−03 4.416 4.146 −135.775 126 20 2 15 −2.630E−05 −1.585E−03 3.302 2.946 −150.237 126 40 2 15 −2.746E−05 −2.560E−04 4.545 4.299 −99.323 126 60 2 15 −2.154E−05 −1.346E−03 4.504 4.208 −152.491 126 20 4 5 −1.512E−04 1.923E−02 6.922 7.427 37.144 126 40 4 5 −3.195E−04 3.478E−02 6.944 7.486 18.837 126 60 4 5 −3.409E−04 5.006E−02 5.617 7.361 56.833 126 20 4 10 −2.020E−04 2.623E−02 6.793 7.518 39.872 126 40 4 10 −5.129E−04 5.197E−02 6.639 7.163 11.334 126 60 4 10 −2.990E−04 4.073E−02 6.153 7.397 46.231 126 20 4 15 −2.123E−04 2.749E−02 6.845 7.599 39.454 126 40 4 15 −9.652E−04 9.178E−02 5.796 6.239 5.095 126 60 4 15 −2.350E−04 2.974E−02 6.625 7.398 36.540 126 20 6 5 −1.027E−03 1.311E−01 6.903 10.383 37.672 126 40 6 5 −7.083E−04 9.295E−02 8.008 10.637 41.229 126 60 6 5 −1.158E−03 1.433E−01 6.235 9.756 33.788 126 20 6 10 −1.271E−03 1.556E−01 6.404 10.111 32.408 126 40 6 10 −1.652E−03 2.052E−01 4.728 9.813 34.190 126 60 6 10 −1.256E−03 1.500E−01 6.185 9.510 29.414 126 20 6 15 −1.394E−03 1.672E−01 6.222 9.972 29.884 126 40 6 15 −1.264E−03 1.551E−01 6.332 10.046 32.641 126 60 6 15 −1.375E−03 1.596E−01 5.971 9.201 26.105 126 20 8 5 −4.670E−04 6.634E−02 11.478 13.667 52.076 126 40 8 5 −1.228E−03 1.832E−01 6.631 13.178 59.247 126 60 8 5 −1.191E−03 1.753E−01 6.679 12.807 57.175 126 20 8 10 −7.326E−04 1.080E−01 9.971 13.759 57.454 126 40 8 10 −1.370E−03 2.032E−01 5.945 13.144 58.399 126 60 8 10 −7.204E−04 1.022E−01 9.485 12.851 51.918 126 20 8 15 −4.069E−04 6.219E−02 11.640 13.941 62.841 126 40 8 15 −2.881E−03 3.499E−01 3.029 11.188 31.470 126 60 8 15 −2.287E−03 2.972E−01 3.685 11.904 39.926

TABLE 8 Thickness Thickness Thickness Lower limit value of groove of first of first of second Stop band angle of region in which Cut dielectric electrode electrode when stop band is larger than or angle layer h/λ layer h/λ layer h/λ groove equal to stop band when (θ) [%] [%] [%] a b c angle = 90° groove angle = 90° (°) 130 20 2 5 −3.946E−05 3.424E−03 3.498 3.487 −3.226 130 20 2 10 −3.586E−05 2.749E−03 3.630 3.587 −13.339 130 20 2 15 −3.701E−05 2.742E−03 3.716 3.663 −15.903 130 40 2 5 −3.188E−05 6.746E−04 4.265 4.068 −68.830 130 40 2 10 −2.679E−05 −2.362E−04 4.407 4.168 −98.817 130 40 2 15 −2.430E−05 −7.477E−04 4.502 4.238 −120.769 130 60 2 5 −2.180E−05 −8.558E−04 4.243 3.990 −129.263 130 60 2 10 −2.024E−05 −1.232E−03 4.367 4.092 −150.859 130 60 2 15 −1.888E−05 −1.566E−03 4.455 4.162 −172.968 130 20 4 5 −9.248E−05 1.011E−02 7.191 7.351 19.304 130 20 4 10 −1.409E−04 1.720E−02 7.038 7.445 32.092 130 20 4 15 −1.685E−04 2.102E−02 6.993 7.521 34.771 130 40 4 5 −2.382E−04 2.619E−02 7.097 7.525 19.958 130 40 4 10 −4.294E−04 4.503E−02 6.712 7.285 14.848 130 40 4 15 −6.656E−04 6.600E−02 6.283 6.832 9.160 130 60 4 5 −2.956E−04 4.260E−02 5.882 7.322 54.137 130 60 4 10 −2.327E−04 3.046E−02 6.505 7.362 40.903 130 60 4 15 −2.454E−04 3.086E−02 6.557 7.347 35.771 130 20 6 5 −9.138E−04 1.176E−01 7.215 10.401 38.738 130 20 6 10 −1.123E−03 1.393E−01 6.762 10.205 34.046 130 20 6 15 −1.349E−03 1.619E−01 6.289 9.933 30.027 130 40 6 5 −6.199E−04 8.046E−02 8.411 10.631 39.799 130 40 6 10 −8.738E−04 1.104E−01 7.573 10.428 36.297 130 40 6 15 −8.290E−04 1.021E−01 7.902 10.378 33.190 130 60 6 5 −4.802E−04 6.662E−02 8.329 10.436 48.749 130 60 6 10 −7.495E−04 9.790E−02 7.471 10.211 40.612 130 60 6 15 −2.921E−04 4.197E−02 9.120 10.532 53.699 130 20 8 5 −6.017E−04 8.377E−02 10.895 13.561 49.232 130 20 8 10 −1.514E−03 2.125E−01 6.478 13.335 50.320 130 20 8 15 −1.020E−03 1.436E−01 8.926 13.590 50.811 130 40 8 5 −1.371E−03 2.055E−01 5.755 13.146 59.907 130 40 8 10 −8.385E−04 1.162E−01 9.484 13.154 48.632 130 40 8 15 −6.586E−04 8.640E−02 10.683 13.124 41.178 130 60 8 5 −9.642E−04 1.365E−01 8.291 12.769 51.599 130 60 8 10 −8.254E−04 1.160E−01 9.022 12.781 50.596 130 60 8 15 −5.505E−04 7.490E−02 10.490 12.772 46.049

TABLE 9 Thickness Thickness Thickness Lower limit value of groove of first of first of second Stop band angle of region in which Cut dielectric electrode electrode when stop band is larger than or angle layer h/λ layer h/λ layer h/λ groove equal to stop band when (θ) [%] [%] [%] a b c angle = 90° groove angle = 90° (°) 134 20 2 5 −3.520E−05 2.970E−03 3.429 3.411 −5.624 134 40 2 5 −2.821E−05 2.517E−04 4.192 3.986 −81.077 134 60 2 5 −1.969E−05 −1.094E−03 4.181 3.924 −145.579 134 20 2 10 −3.415E−05 2.643E−03 3.549 3.510 −12.618 134 40 2 10 −2.308E−05 −6.724E−04 4.335 4.088 −119.139 134 60 2 10 −1.832E−05 −1.433E−03 4.303 4.026 −168.228 134 20 2 15 −3.365E−05 2.470E−03 3.639 3.588 −16.587 134 40 2 15 −2.165E−05 −1.030E−03 4.427 4.159 −137.565 134 60 2 15 −1.703E−05 −1.730E−03 4.391 4.098 −191.581 134 20 4 5 −9.042E−05 9.811E−03 7.079 7.229 18.495 134 40 4 5 −1.862E−04 2.057E−02 7.148 7.491 20.488 134 60 4 5 −4.328E−04 4.557E−02 6.245 6.840 15.282 134 20 4 10 −1.171E−04 1.381E−02 7.033 7.327 27.895 134 40 4 10 −2.767E−04 2.960E−02 7.001 7.424 16.973 134 60 4 10 −3.342E−04 4.432E−02 5.979 7.261 42.606 134 20 4 15 −1.179E−04 1.379E−02 7.122 7.408 26.985 134 40 4 15 −4.279E−04 4.407E−02 6.694 7.194 12.979 134 60 4 15 −2.240E−04 2.635E−02 6.704 7.261 27.640 134 20 6 5 −7.885E−04 1.025E−01 7.538 10.379 40.024 134 40 6 5 −4.789E−04 6.077E−02 9.027 10.618 36.904 134 60 6 5 −9.441E−04 1.172E−01 6.927 9.832 34.187 134 20 6 10 −1.054E−03 1.318E−01 6.837 10.161 35.043 134 40 6 10 −6.395E−04 8.044E−02 8.458 10.518 35.787 134 60 6 10 −9.782E−04 1.195E−01 6.920 9.754 32.178 134 20 6 15 −1.163E−03 1.427E−01 6.650 10.071 32.694 134 40 6 15 −9.023E−04 1.114E−01 7.547 10.261 33.420 134 60 6 15 −5.839E−04 7.768E−02 7.982 10.244 43.045 134 20 8 5 −1.029E−03 1.439E−01 8.718 13.333 49.832 134 40 8 5 −1.802E−03 2.316E−01 6.180 12.426 38.511 134 60 8 5 −1.663E−03 2.239E−01 5.724 12.402 44.614 134 20 8 10 −1.962E−03 2.534E−01 5.607 12.522 39.151 134 40 8 10 −2.430E−03 3.067E−01 3.953 11.871 36.208 134 60 8 10 −8.940E−04 1.251E−01 8.702 12.715 49.871 134 20 8 15 −1.453E−03 1.997E−01 7.050 13.252 47.435 134 40 8 15 −1.999E−03 2.547E−01 5.496 12.225 37.404 134 60 8 15 −6.711E−04 9.073E−02 9.948 12.678 45.209

TABLE 10 Thickness Thickness Thickness Lower limit value of groove of first of first of second Stop band angle of region in which Cut dielectric electrode electrode when stop band is larger than or angle layer h/λ layer h/λ layer h/λ groove equal to stop band when (θ) [%] [%] [%] a b c angle = 90° groove angle = 90° (°) 138 20 2 5 −3.200E−05 2.565E−03 3.353 3.324 −9.844 138 40 2 5 −5.260E−05 4.305E−03 3.918 3.880 −8.156 138 60 2 5 −1.801E−05 −1.218E−03 4.103 3.847 −157.625 138 20 2 10 −3.040E−05 2.278E−03 3.468 3.427 −15.068 138 40 2 10 −2.702E−05 1.746E−04 4.190 3.987 −83.538 138 60 2 10 −1.661E−05 −1.555E−03 4.223 3.948 −183.664 138 20 2 15 −2.979E−05 2.123E−03 3.554 3.504 −18.741 138 40 2 15 −2.239E−05 −7.013E−04 4.306 4.061 −121.326 138 60 2 15 −1.532E−05 −1.845E−03 4.311 4.021 −210.441 138 20 4 5 −7.468E−05 7.958E−03 6.961 7.073 16.563 138 40 4 5 −1.649E−04 1.855E−02 7.067 7.401 22.513 138 60 4 5 −2.783E−04 3.053E−02 6.508 7.002 19.695 138 20 4 10 −1.115E−04 1.365E−02 6.847 7.173 32.489 138 40 4 10 −2.565E−04 2.803E−02 6.904 7.349 19.304 138 60 4 10 −6.118E−04 3.455E−03 7.418 7.233 −33.524 138 20 4 15 −1.704E−04 2.169E−02 6.659 7.231 37.283 138 40 4 15 −2.538E−04 2.683E−02 6.998 7.357 15.705 138 60 4 15 −1.039E−04 9.485E−03 7.211 7.224 1.302 138 20 6 5 −7.650E−04 1.004E−01 7.402 10.246 41.300 138 40 6 5 −5.949E−04 7.764E−02 8.324 10.493 40.508 138 60 6 5 −8.809E−04 1.095E−01 7.074 9.797 34.352 138 20 6 10 −8.485E−04 1.090E−01 7.289 10.223 38.407 138 40 6 10 −1.033E−03 1.247E−01 7.132 9.984 30.668 138 60 6 10 −8.972E−04 1.104E−01 7.092 9.761 33.045 138 20 6 15 −1.015E−03 1.269E−01 6.889 10.088 35.005 138 40 6 15 −5.068E−04 6.197E−02 8.982 10.454 32.282 138 60 6 15 −1.015E−03 1.219E−01 6.781 9.530 30.100 138 20 8 5 −1.565E−03 2.187E−01 6.047 13.051 49.732 138 40 8 5 −1.334E−03 1.815E−01 7.384 12.910 46.016 138 60 8 5 −6.407E−04 8.409E−02 10.325 12.703 41.243 138 20 8 10 −1.303E−03 1.821E−01 7.351 13.192 49.820 138 40 8 10 −1.284E−03 1.734E−01 7.681 12.886 45.024 138 60 8 10 −1.159E−03 1.599E−01 7.556 12.559 47.975 138 20 8 15 −1.374E−03 1.916E−01 7.106 13.227 49.511 138 40 8 15 −1.957E−03 2.472E−01 5.686 12.084 36.321 138 60 8 15 −7.031E−04 9.422E−02 9.816 12.600 43.993

TABLE 11 Thickness Thickness Thickness Lower limit value of groove of first of first of second Stop band angle of region in which Cut dielectric electrode electrode when stop band is larger than or angle layer h/λ layer h/λ layer h/λ groove equal to stop band when (θ) [%] [%] [%] a b c angle = 90° groove angle = 90° (°) 142 20 2 5 −2.767E−05 2.108E−03 3.270 3.236 −13.808 142 40 2 5 −7.500E−05 8.176E−03 3.623 3.752 19.022 142 60 2 5 −1.714E−05 −1.116E−03 4.004 3.760 −158.006 142 20 2 10 −2.653E−05 1.881E−03 3.379 3.334 −19.109 142 40 2 10 −3.745E−05 2.205E−03 3.971 3.866 −31.118 142 60 2 10 −1.522E−05 −1.567E−03 4.124 3.859 −192.937 142 20 2 15 −2.585E−05 1.771E−03 3.461 3.411 −21.493 142 40 2 15 −2.586E−05 1.809E−04 4.137 3.944 −83.003 142 60 2 15 −1.378E−05 −1.876E−03 4.213 3.932 −226.131 142 20 4 5 −9.928E−05 1.306E−02 6.503 6.874 41.532 142 40 4 5 −1.573E−04 1.836E−02 6.898 7.277 26.742 142 60 4 5 −2.148E−04 2.498E−02 6.509 7.018 26.303 142 20 4 10 −1.399E−04 1.914E−02 6.385 6.975 46.866 142 40 4 10 −1.486E−04 1.674E−02 7.041 7.344 22.693 142 60 4 10 −1.682E−04 1.840E−02 6.788 7.082 19.364 142 20 4 15 −1.508E−04 2.055E−02 6.427 7.055 46.258 142 40 4 15 −1.160E−04 1.254E−02 7.214 7.403 18.107 142 60 4 15 −1.159E−04 1.148E−02 7.018 7.112 9.057 142 20 6 5 −8.279E−04 1.131E−01 6.641 10.110 46.556 142 40 6 5 −5.491E−04 7.239E−02 8.309 10.376 41.829 142 60 6 5 −4.923E−04 6.647E−02 8.120 10.114 45.022 142 20 6 10 −8.281E−04 1.091E−01 6.985 10.096 41.746 142 40 6 10 −5.833E−04 7.580E−02 8.261 10.358 39.943 142 60 6 10 −5.093E−04 6.782E−02 8.118 10.097 43.178 142 20 6 15 −1.007E−03 1.290E−01 6.520 9.969 38.054 142 40 6 15 −4.728E−04 6.178E−02 8.710 10.441 40.669 142 60 6 15 −6.206E−04 8.039E−02 7.744 9.952 39.531 142 20 8 5 −1.358E−03 1.925E−01 6.587 12.918 51.802 142 40 8 5 −1.298E−03 1.776E−01 7.330 12.805 46.877 142 60 8 5 −1.260E−03 1.750E−01 6.940 12.488 48.943 142 20 8 10 −2.695E−03 3.481E−01 2.263 11.763 39.168 142 40 8 10 −1.286E−03 1.749E−01 7.459 12.790 46.073 142 60 8 10 −1.246E−03 1.721E−01 7.059 12.453 48.102 142 20 8 15 −1.976E−03 2.590E−01 5.034 12.333 41.041 142 40 8 15 −1.317E−03 1.787E−01 7.322 12.741 45.733 142 60 8 15 −1.223E−03 1.688E−01 7.108 12.392 47.985

Next, regarding the case where the piezoelectric substrate 10 was made of a LiTaO₃ substrate, the range of the groove angle, in which the stop band was able to be made larger than the stop band when the groove angle was 90°, was calculated from the results shown in Table 7 to Table 11 and the range of the groove angles which were able to be formed physically. The calculation results are shown in Tables 12 to 15 described below.

Concretely, the lower limit of the groove angle in which the cross-sectional shape of the groove was trapezoidal was about 10°, where the depth of the groove normalized by the wave length was 2% and the duty was 0.4 to 0.6. Consequently, for example, in the case where the lower limit value of the groove angle of the region in which the stop band was larger than or equal to the stop band when the groove angle was 90° was larger than 10°, the lower limit value of the groove angle of the region in which the stop band was larger than or equal to the stop band when the groove angle was 90° was adopted as the lower limit value of the range of the groove angle in which the stop band was able to become larger than the stop band when the groove angle was 90°. Meanwhile, in the case where the lower limit value of the groove angle of the region in which the stop band was larger than or equal to the stop band when the groove angle was 90° was less than 10°, the lower limit value of the range of the groove angle in which the stop band was able to become larger than the stop band when the groove angle was 90° was specified to be 10°.

As is clear from the above description, in the case where the piezoelectric substrate 10 is made of the LiTaO₃ substrate, the stop band can be increased by specifying θ of the Euler Angles (φ, θ, φ) and the groove angle γ to be within the range stipulated in Tables 12 to 15 described below.

In this regard, each of φ and φ of the above-described data is specified to be 0°, and it is well known to a person skilled in the art that the data with respect to 0° can be applied to the range of 0°±5° in general.

TABLE 12 Thickness of first θ of Euler Angles Thickness of first Thickness of second dielectric layer h/λ [%] (φ, θ, φ) [°] electrode layer h/λ [%] electrode layer h/λ [%] Groove angle [°] 10 < h < λ ≦ 30 124 < θ ≦ 128 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 37.1 ≦ γ < 90.0  7.5 < Al ≦ 12.5 39.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 39.5 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 37.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 32.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5 29.9 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 52.1 ≦ γ < 90.0  7.5 < Al ≦ 12.5 57.5 ≦ γ < 90.0 12.5 < Al ≦ 17.5 62.8 ≦ γ < 90.0 128 < θ ≦ 132 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 19.3 ≦ γ < 90.0  7.5 < Al ≦ 12.5 32.1 ≦ γ < 90.0 12.5 < Al ≦ 17.5 34.8 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 38.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5   34 ≦ γ < 90.0 12.5 < Al ≦ 17.5   30 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 49.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 50.3 ≦ γ < 90.0 12.5 < Al ≦ 17.5 50.8 ≦ γ < 90.0 132 < θ ≦ 136 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 18.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 27.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5   27 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5   40 ≦ γ < 90.0  7.5 < Al ≦ 12.5   35 ≦ γ < 90.0 12.5 < Al ≦ 17.5 32.7 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 49.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 39.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 47.4 ≦ γ < 90.0 136 < θ ≦ 140 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 18.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 32.5 ≦ γ < 90.0 12.5 < Al ≦ 17.5 37.3 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 41.3 ≦ γ < 90.0  7.5 < Al ≦ 12.5 38.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5   35 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 49.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 49.8 ≦ γ < 90.0 12.5 < Al ≦ 17.5 49.5 ≦ γ < 90.0

TABLE 13 Thickness of first θ of Euler Angles Thickness of first Thickness of second dielectric layer h/λ [%] (φ, θ, φ) [°] electrode layer h/λ [%] electrode layer h/λ [%] Groove angle [°] 10 < h < λ ≦ 30 140 < θ ≦ 144 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 41.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 46.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 46.3 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 46.6 ≦ γ < 90.0  7.5 < Al ≦ 12.5 41.7 ≦ γ < 90.0 12.5 < Al ≦ 17.5 38.1 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 51.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 39.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5   41 ≦ γ < 90.0 30 < h < λ ≦ 50 124 < θ ≦ 128 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 18.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 18.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 41.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 34.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 32.6 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 59.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 58.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5 33.0 ≦ γ < 90.0 128 < θ ≦ 132 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5   20 ≦ γ < 90.0  7.5 < Al ≦ 12.5 18.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 39.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 36.3 ≦ γ < 90.0 12.5 < Al ≦ 17.5 33.2 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 59.9 ≦ γ < 90.0  7.5 < Al ≦ 12.5 48.6 ≦ γ < 90.0 12.5 < Al ≦ 17.5 41.2 ≦ γ < 90.0 132 < θ ≦ 136 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 20.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 18.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 36.9 ≦ γ < 90.0  7.5 < Al ≦ 12.5 35.8 ≦ γ < 90.0 12.5 < Al ≦ 17.5 33.4 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 38.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 36.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 37.4 ≦ γ < 90.0

TABLE 14 Thickness of first θ of Euler Angles Thickness of first Thickness of second dielectric layer h/λ [%] (φ, θ, φ) [°] electrode layer h/λ [%] electrode layer h/λ [%] Groove angle [°] 30 < h < λ ≦ 50 136 < θ ≦ 140 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 22.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 19.3 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 40.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 30.7 ≦ γ < 90.0 12.5 < Al ≦ 17.5 32.3 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5   46 ≦ γ < 90.0  7.5 < Al ≦ 12.5   45 ≦ γ < 90.0 12.5 < Al ≦ 17.5 36.3 ≦ γ < 90.0 140 < θ ≦ 144 1 < Pt ≦ 3 2.5 < Al ≦ 7.5   19 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 26.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 22.7 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.1 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 41.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 39.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 40.7 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 46.9 ≦ γ < 90.0  7.5 < Al ≦ 12.5 46.1 ≦ γ < 90.0 12.5 < Al ≦ 17.5 45.7 ≦ γ < 90.0 50 < h < λ ≦ 70 124 < θ ≦ 128 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 56.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 46.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 36.5 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 33.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 29.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5 26.1 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 57.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 51.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 39.9 ≦ γ < 90.0 128 < θ ≦ 132 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 54.1 ≦ γ < 90.0  7.5 < Al ≦ 12.5 40.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 35.8 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 48.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 40.6 ≦ γ < 90.0 12.5 < Al ≦ 17.5 53.7 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 51.6 ≦ γ < 90.0  7.5 < Al ≦ 12.5 50.6 ≦ γ < 90.0 12.5 < Al ≦ 17.5   46 ≦ γ < 90.0

TABLE 15 Thickness of first θ of Euler Angles Thickness of first Thickness of second dielectric layer h/λ [%] (φ, θ, φ) [°] electrode layer h/λ [%] electrode layer h/λ [%] Groove angle [°] 50 < h < λ ≦ 70 132 < θ ≦ 136 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 18.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 42.6 ≦ γ < 90.0 12.5 < Al ≦ 17.5 27.6 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 34.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 32.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5   43 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 44.6 ≦ γ < 90.0  7.5 < Al ≦ 12.5 49.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 45.2 ≦ γ < 90.0 136 < θ ≦ 140 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 19.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 18.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 34.4 ≦ γ < 90.0  7.5 < Al ≦ 12.5   33 ≦ γ < 90.0 12.5 < Al ≦ 17.5 30.1 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 41.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5   48 ≦ γ < 90.0 12.5 < Al ≦ 17.5   44 ≦ γ < 90.0 140 < θ ≦ 144 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 26.3 ≦ γ < 90.0  7.5 < Al ≦ 12.5 19.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5   45 ≦ γ < 90.0  7.5 < Al ≦ 12.5 43.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 39.5 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 48.9 ≦ γ < 90.0  7.5 < Al ≦ 12.5 48.1 ≦ γ < 90.0 12.5 < Al ≦ 17.5   48 ≦ γ < 90.0

Meanwhile, in the case where the piezoelectric substrate 10 is LiNbO₃, it is preferable that −5°≦φ≦+5°, +80°≦θ≦+130°, −10°≦φ≦+10°, and 10°≦γ<90° are satisfied, where the Euler Angles of the piezoelectric substrate are specified to be (φ, θ, φ) and the groove angle is specified to be γ. According to this configuration, in the case where the piezoelectric substrate 10 is made of LiNbO₃ and a boundary acoustic wave in the SH (Shear Horizontal) mode is utilized, the stop band can be further increased. Moreover, a propagation loss of the boundary acoustic wave can be reduced particularly, and an occurrence of unnecessary spurious response can be suppressed effectively.

FIG. 80 to FIG. 84 show the relationship between the groove angle (γ) and the stop band, where the cross-sectional shape is as shown in FIG. 17 and the piezoelectric substrate is made of LiNbO₃. In this regard, the design parameters of the data shown in FIG. 80 to FIG. 84 are as described below.

Piezoelectric substrate 10: LiNbO₃ substrate having

Euler Angles (φ, θ, φ) of (0, 85°, 0), (0, 95°, 0), (0, 105°, 0), (0, 115°, 0), or (0, 125°, 0)

Electrode finger ratio (duty) of IDT electrode 13: 0.5

First dielectric layer 11: SiO₂ layer (film thickness normalized by wave length: 60%)

First electrode layer 13 a; Pt layer (film thickness normalized by wave length: 4%)

Second electrode layer 13 b; Al layer (film thickness normalized by wave length: 10%)

First to third diffusion preventing films 13 c to 13 e; Ti film (film thickness normalized by wave length: 0.5%)

Meanwhile, in the case where the piezoelectric substrate 10 is LiNbO₃, it is preferable that −5°≦φ≦+5°, +200°≦θ≦+250°, −10°≦φ≦+10°, and 10°≦γ<90° are satisfied. According to this configuration, in the case where the piezoelectric substrate 10 is made of LiNbO₃ and a boundary acoustic wave in the Stoneley mode is utilized, the stop band can be further increased. Moreover, a propagation loss of the boundary acoustic wave can be reduced particularly, and an occurrence of unnecessary spurious response can be suppressed effectively.

FIG. 85 to FIG. 89 show the relationship between the groove angle (γ) and the stop band, where the cross-sectional shape is as shown in FIG. 17 and the piezoelectric substrate is made of LiNbO₃. In this regard, the design parameters of the data shown in FIG. 85 to FIG. 89 are as described below.

Piezoelectric substrate 10: LiNbO₃ substrate having

Euler Angles (φ, θ, φ) of (0, 205°, 0), (0, 215°, 0), (0, 225°, 0), (0, 235°, 0), or (0, 245°, 0)

Electrode finger ratio (duty) of IDT electrode 13: 0.5

First dielectric layer 11: SiO₂ layer (film thickness normalized by wave length: 60%)

First electrode layer 13 a; Pt layer (film thickness normalized by wave length: 4%)

Second electrode layer 13 b; Al layer (film thickness normalized by wave length: 10%)

First to third diffusion preventing films 13 c to 13 e; Ti film (film thickness normalized by wave length: 0.5%)

In this regard, in the present specification, Euler Angles, a crystallographic axis, and equivalent Euler Angles refer to the following.

(Euler Angles)

In the present specification, as for the Euler Angles (φ, θ, φ) which express the cutting plane of the substrate and the propagation direction of the boundary wave, the right-handed Euler Angles described in a literature, “Danseiha Soshi Gijutu Handobukku (Acoustic Wave Device Technology Handbook)” (the Japan Society for the Promotion of Science, Committee for Acoustic Wave Device Technology 150, First copy, First edition, Issued on Jan. 30, 1991, p. 549) was used.

That is, for example, regarding the crystallographic axes X, Y, and Z of LiNbO₃, the X axis was turned about the Z axis by a φ turn counter-clockwise, so as to obtain an Xa axis.

Next, the Z axis was turned about the Xa axis by a θ turn counter-clockwise, so as to obtain a Z′ axis.

The cutting plane of the substrate was specified to be the plane including the Xa axis, where the Z′ axis was the normal to the plane.

Then, the direction of the X′ axis obtained by turning the Xa axis about the Z′ axis by a φ turn counter-clockwise was specified to be the propagation direction of the boundary wave.

(Crystallographic Axis)

Furthermore, the crystallographic axes X, Y, and Z axes given as initial values of the Euler Angles are specified to be parallel to the c axis, the X axis is specified to be parallel to any one of a axes in three equivalent directions, and the Y axis is specified to be in the direction of normal to the plane including the X axis and the Z axis.

(Equivalent Euler Angles)

In this regard, it is essential only that the Euler Angles (φ, θ, φ) in the present invention are crystallographically equivalent.

For example, according to a literature (the Journal of Acoustical Society of Japan, Vol. 36, No. 3, 1980, p. 140-145), LiNbO₃ and LiTaO₃ are crystals belonging to trigonal system 3 m point group and, therefore, Formula [1] holds.

$\begin{matrix} {{F\left( {\varphi,\theta,\phi} \right)} = {{F\left( {{{60{^\circ}} - \varphi},{- \theta},{{180{^\circ}} - \phi}} \right)} = {{F\left( {{{60{^\circ}} + \varphi},{- \theta},\phi} \right)} = {{F\left( {\varphi,{{180{^\circ}} + \theta},{{180{^\circ}} - \phi}} \right)} = {F\left( {\varphi,\theta,{{180{^\circ}} + \phi}} \right)}}}}} & \lbrack 1\rbrack \end{matrix}$

Here, F represents any boundary wave characteristic, e.g., an electromechanical coupling coefficient k_(s) ², a propagation loss, TCF, PFA, or natural unidirectionality.

It is believed that the natural unidirectionality of PFA, for example, in the case where the positive direction and the negative direction of propagation are reversed, is equivalent in practice because the absolute values are equal, although the sign is changed.

In this regard, the above-described literature relates to the surface acoustic wave. However, the symmetry of crystal is treated in the same manner regarding the boundary wave.

For example, the boundary wave propagation characteristics of the Euler Angles (30°,θ,φ) are equivalent to the boundary wave propagation characteristics of the Euler Angles (90°, 180°−θ, 180°−φ).

Moreover, for example, the boundary wave propagation characteristics of the Euler Angles)(30°, 90°, 45°) are equivalent to the boundary wave propagation characteristics of the Euler Angles shown in Table 16.

In this regard, the material constant of the conductor used for calculation in the present invention is a value of a polycrystal. However, regarding crystals, e.g., epitaxial films, as well, the crystal orientation dependence of the substrate is predominant over the boundary wave characteristics as compared with the crystal orientation dependence of the film in itself. Therefore, the boundary wave propagation characteristics at the same level to the extent that cause no problem in practice are obtained on the basis of Formula [1].

TABLE 16 φ (°) θ (°) ψ (°) 30 90 225 30 270 135 30 270 315 90 90 135 90 90 315 90 270 45 90 270 225 150 90 45 150 90 225 150 270 135 150 270 315 210 90 135 210 90 315 210 270 45 210 270 225 270 90 45 270 90 225 270 270 135 270 270 315 330 90 135 330 90 315 330 270 45 330 270 225

(Other Modified Preferred Embodiments)

In the above-described preferred embodiments, the three-media boundary acoustic wave device formed from a piezoelectric material, and the first and the second dielectric layers is explained. However, the boundary acoustic wave device according to the present invention is not limited to the three-media boundary acoustic wave device. The boundary acoustic wave device according to the present invention may be a two-media boundary acoustic wave device not including the second dielectric layer. In this regard, in the case where the second dielectric layer is disposed, an insertion loss can be reduced because of a waveguide effect and, therefore, it is preferable that the boundary acoustic wave device according to the present invention is the three-media boundary acoustic wave device.

In the present invention, the IDT electrode structure is not limited to the structures shown in the above-described preferred embodiment and the first modified preferred embodiment. The IDT electrode may have, for example, structures as shown in FIG. 11 to FIG. 16.

In the example shown in FIG. 11, the IDT electrode 13 is formed from a first diffusion preventing film 13 c disposed in a groove 10 a on a piezoelectric substrate 10 a, first electrode layer 13 a disposed on the first diffusion preventing film 13 c, a second electrode layer 13 b disposed on the first electrode layer 13 a, and a second diffusion preventing film 13 d disposed between the first electrode layer 13 a and the second electrode layer 13 b. Then, all the first and the second electrode layers 13 a and 13 b and the first and the second diffusion preventing films 13 c and 13 d are disposed in the groove 10 a. As shown in FIG. 11, diffusion of the electrode material from the electrode layers 13 a and 13 b can be prevented by disposing the diffusion preventing films 13 c and 13 d between the electrode layers 13 a and 13 b adjacent to each other and between the electrode layer 13 a and the piezoelectric substrate 10. Furthermore, the adhesion between the electrode layers 13 a and 13 b can be enhanced.

The material for the diffusion preventing films 13 c and 13 d is not specifically limited. For example, the diffusion preventing films 13 c and 13 d can be made of, for example, at least one type of metal selected from the group consisting of Ti, Ni, Cr, and Ta or an alloy containing at least one type of metal selected from the group consisting of Ti, Ni, Cr, and Ta.

Alternatively, in the example shown in FIG. 12, only a first electrode layer 13 a is disposed as the electrode layer, and a first diffusion preventing film 13 c is disposed between the first electrode layer 13 a and the piezoelectric substrate 10. A part of the first electrode layer 13 a is located in the groove 10 a, and the remainder portion is located outside the groove 10 a.

Regarding the example shown in FIG. 13, as in the example shown in FIG. 12, the IDT electrode 13 is formed from a first electrode layer 13 a and a first diffusion preventing film 13 c. In the example shown in FIG. 13, the surface of the central portion of the first electrode layer 13 a is flush with the surface 10 b of a piezoelectric substrate 10, and a portion excluding the end portion of the first electrode layer 13 a is located in the groove 10 a.

Regarding the example shown in FIG. 14, as in the example shown in FIG. 11, the IDT electrode 13 is formed from first and second electrode layers 13 a and 13 b and first and second diffusion preventing films 13 c and 13 d. In the example shown in FIG. 11, the whole IDT electrode 13 is located in the groove 10 a. However, in the example shown in FIG. 14, a part of the first electrode layer 13 a, the second diffusion preventing film 13 d, and the second electrode layer 13 b are located outside the groove 10 a. Consequently, in the example shown in FIG. 14, in the inside of the groove 10 a, only the first electrode layer 13 a made of a high-density electrically conductive material is located, and the second electrode layer 13 b made of a low-density electrically conductive material is not located.

Regarding the example shown in FIG. 15 as well, as in the example shown in FIG. 11 and the example shown in FIG. 14, the IDT electrode 13 is formed from first and second electrode layers 13 a and 13 b and first and second diffusion preventing films 13 c and 13 d. In the example shown in FIG. 15, only the first electrode layer 13 a made of a high-density electrically conductive material of the first and the second electrode layers 13 a and 13 b is located in the groove 10 a, and the second electrode layer 13 b is located outside the groove 10 a. Concretely, the first electrode layer 13 a and the first and the second diffusion preventing films 13 c and 13 d are located in the groove 10 a, and the second electrode layer 13 b is located outside the groove 10 a.

Regarding the example shown in FIG. 16 as well, as in the examples shown in FIGS. 11, 14 and 15, the IDT electrode 13 is formed from first and second electrode layers 13 a and 13 b and first and second diffusion preventing films 13 c and 13 d. In the example shown in FIG. 16, a part of each of the first and the second electrode layers 13 a and 13 b is located in the groove 10 a. That is, a part of the second electrode layer 13 b made of a low-density electrically conductive material is also located in the groove 10 a.

In this regard, in the examples shown in FIGS. 11 to 16, the case where only the first and the second electrode layers 13 a and 13 b are included as the electrode layers is explained. However, the IDT electrode 13 may include at least three electrode layers.

Meanwhile, the boundary acoustic wave device according to the present invention may be, for example, a resonator or a filter device.

Furthermore, the cross-sectional shape of the groove disposed in the piezoelectric substrate is not specifically limited to the trapezoidal shape and may be a semi-elliptic shape, a semi-oval shape, a triangular shape, or the like.

Moreover, it is essential only that the angle formed by the upper end portion of the inside surface of the groove with the surface of the piezoelectric substrate is less than 90 degrees, and a portion which forms an angle of 90° or more with the surface of the piezoelectric substrate may be present as a part of the inside surface of the groove.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

1. A boundary acoustic wave device comprising: a piezoelectric substrate having a surface provided with a groove; a first dielectric layer disposed on the surface of the piezoelectric substrate; and an IDT electrode disposed at the boundary between the piezoelectric substrate and the first dielectric layer in such a way that at least a part thereof is located in the groove, wherein in the inside of the groove, the groove angle, which is the size of an angle formed by an upper end portion of the inside surface of the groove with the surface of the piezoelectric substrate, is less than 90 degrees.
 2. The boundary acoustic wave device according to claim 1, wherein a part of the IDT electrode is located outside the groove, and the portion, which is located outside the groove, of the IDT electrode is tapered with decreasing away from the piezoelectric substrate.
 3. The boundary acoustic wave device according to clam 1, further comprising a second dielectric layer which is disposed on the first dielectric layer and which has an acoustic velocity larger than that of the first dielectric layer.
 4. The boundary acoustic wave device according to claim 3, wherein each of the first and the second dielectric layers is made of silicon oxide, silicon nitride, or aluminum nitride.
 5. The boundary acoustic wave device according to claim 1, wherein the average density of the portion, which is located in the groove, of the IDT electrode is higher than the average density of the piezoelectric substrate.
 6. The boundary acoustic wave device according to claim 1, wherein at least a part of the portion, which is located in the groove, of the IDT electrode is made of at least one type of metal selected from the group consisting of Pt, Au, W, Ta, Mo, Ni, and Cu or an alloy containing at least one type of metal selected from the group consisting of Pt, Au, W, Ta, Mo, Ni, and Cu.
 7. The boundary acoustic wave device according to claim 1, wherein the IDT electrode is formed from a laminate of a plurality of electrode layers, and the resistivity of at least one layer of the plurality of electrode layers is 5 μΩcm or less.
 8. The boundary acoustic wave device according to claim 7, wherein the electrode layer having a resistivity of 5 μΩcm or less is made of at least one type of metal selected from the group consisting of Al, Cu, Au, and Ag or an alloy containing at least one type of metal selected from the group consisting of Al, Cu, Au, and Ag.
 9. The boundary acoustic wave device according to claim 1, wherein the IDT electrode is formed from a laminate of a plurality of electrode layers, and a diffusion preventing film is disposed in at least one of a place between the IDT electrode and the bottom of the groove and a place between the electrode layers adjacent to each other.
 10. The boundary acoustic wave device according to claim 9, wherein the diffusion preventing film is made of at least one type of metal selected from the group consisting of Ti, Ni, Cr, and Ta or an alloy containing at least one type of metal selected from the group consisting of Ti, Ni, Cr, and Ta.
 11. The boundary acoustic wave device according to claim 1, wherein the piezoelectric substrate is made of LiTaO₃.
 12. The boundary acoustic wave device according to claim 11, wherein the IDT electrode includes a first electrode layer, which is located in the groove of the piezoelectric substrate and which contains Pt, and a second electrode layer, which is located outside the groove of the piezoelectric substrate and which contains Al, and the first dielectric layer is made of silicon oxide, and wherein θ of the Euler Angles (φ, θ, φ) and the groove angle γ are within the range specified in Tables 1 to 4 described below and each of φ and φ of the Euler Angles is within the range of 0° ±5°, where the Euler Angles of the piezoelectric substrate are specified to be (φ, θ, φ) and the groove angle is specified to be γ TABLE 1 Thickness of first θ of Euler Angles Thickness of first Thickness of second dielectric layer h/λ [%] (φ, θ, φ) [°] electrode layer h/λ [%] electrode layer h/λ [%] Groove angle [°] 10 < h < λ ≦ 30 124 < θ ≦ 128 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 37.1 ≦ γ < 90.0  7.5 < Al ≦ 12.5 39.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 39.5 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 37.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 32.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5 29.9 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 52.1 ≦ γ < 90.0  7.5 < Al ≦ 12.5 57.5 ≦ γ < 90.0 12.5 < Al ≦ 17.5 62.8 ≦ γ < 90.0 128 < θ ≦ 132 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 19.3 ≦ γ < 90.0  7.5 < Al ≦ 12.5 32.1 ≦ γ < 90.0 12.5 < Al ≦ 17.5 34.8 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 38.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5   34 ≦ γ < 90.0 12.5 < Al ≦ 17.5   30 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 49.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 50.3 ≦ γ < 90.0 12.5 < Al ≦ 17.5 50.8 ≦ γ < 90.0 132 < θ ≦ 136 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 18.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 27.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5   27 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5   40 ≦ γ < 90.0  7.5 < Al ≦ 12.5   35 ≦ γ < 90.0 12.5 < Al ≦ 17.5 32.7 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 49.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 39.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 47.4 ≦ γ < 90.0 136 < θ ≦ 140 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 18.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 32.5 ≦ γ < 90.0 12.5 < Al ≦ 17.5 37.3 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 41.3 ≦ γ < 90.0  7.5 < Al ≦ 12.5 38.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5   35 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 49.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 49.8 ≦ γ < 90.0 12.5 < Al ≦ 17.5 49.5 ≦ γ < 90.0

TABLE 2 Thickness of first θ of Euler Angles Thickness of first Thickness of second dielectric layer h/λ [%] (φ, θ, φ) [°] electrode layer h/λ [%] electrode layer h/λ [%] Groove angle [°] 10 < h < λ ≦ 30 140 < θ ≦ 144 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 41.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 46.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 46.3 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 46.6 ≦ γ < 90.0  7.5 < Al ≦ 12.5 41.7 ≦ γ < 90.0 12.5 < Al ≦ 17.5 38.1 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 51.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 39.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5   41 ≦ γ < 90.0 30 < h < λ ≦ 50 124 < θ ≦ 128 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 18.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 18.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 41.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 34.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 32.6 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 59.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 58.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5 33.0 ≦ γ < 90.0 128 < θ ≦ 132 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5   20 ≦ γ < 90.0  7.5 < Al ≦ 12.5 18.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 39.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 36.3 ≦ γ < 90.0 12.5 < Al ≦ 17.5 33.2 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 59.9 ≦ γ < 90.0  7.5 < Al ≦ 12.5 48.6 ≦ γ < 90.0 12.5 < Al ≦ 17.5 41.2 ≦ γ < 90.0 132 < θ ≦ 136 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 20.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 18.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 36.9 ≦ γ < 90.0  7.5 < Al ≦ 12.5 35.8 ≦ γ < 90.0 12.5 < Al ≦ 17.5 33.4 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 38.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 36.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 37.4 ≦ γ < 90.0

TABLE 3 Thickness of first θ of Euler Angles Thickness of first Thickness of second dielectric layer h/λ [%] (φ, θ, φ) [°] electrode layer h/λ [%] electrode layer h/λ [%] Groove angle [°] 30 < h < λ ≦ 50 136 < θ ≦ 140 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 22.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 19.3 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 40.5 ≦ γ < 90.0  7.5 < Al ≦ 12.5 30.7 ≦ γ < 90.0 12.5 < Al ≦ 17.5 32.3 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5   46 ≦ γ < 90.0  7.5 < Al ≦ 12.5   45 ≦ γ < 90.0 12.5 < Al ≦ 17.5 36.3 ≦ γ < 90.0 140 < θ ≦ 144 1 < Pt ≦ 3 2.5 < Al ≦ 7.5   19 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 26.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 22.7 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.1 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 41.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 39.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 40.7 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 46.9 ≦ γ < 90.0  7.5 < Al ≦ 12.5 46.1 ≦ γ < 90.0 12.5 < Al ≦ 17.5 45.7 ≦ γ < 90.0 50 < h < λ ≦ 70 124 < θ ≦ 128 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 56.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 46.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 36.5 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 33.8 ≦ γ < 90.0  7.5 < Al ≦ 12.5 29.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5 26.1 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 57.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 51.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 39.9 ≦ γ < 90.0 128 < θ ≦ 132 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 54.1 ≦ γ < 90.0  7.5 < Al ≦ 12.5 40.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 35.8 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 48.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 40.6 ≦ γ < 90.0 12.5 < Al ≦ 17.5 53.7 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 51.6 ≦ γ < 90.0  7.5 < Al ≦ 12.5 50.6 ≦ γ < 90.0 12.5 < Al ≦ 17.5   46 ≦ γ < 90.0

TABLE 4 Thickness of first θ of Euler Angles Thickness of first Thickness of second dielectric layer h/λ [%] (φ, θ, φ) [°] electrode layer h/λ [%] electrode layer h/λ [%] Groove angle [°] 50 < h < λ ≦ 70 132 < θ ≦ 136 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 18.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 42.6 ≦ γ < 90.0 12.5 < Al ≦ 17.5 27.6 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 34.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5 32.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5   43 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 44.6 ≦ γ < 90.0  7.5 < Al ≦ 12.5 49.9 ≦ γ < 90.0 12.5 < Al ≦ 17.5 45.2 ≦ γ < 90.0 136 < θ ≦ 140 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 19.7 ≦ γ < 90.0  7.5 < Al ≦ 12.5 18.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5 34.4 ≦ γ < 90.0  7.5 < Al ≦ 12.5   33 ≦ γ < 90.0 12.5 < Al ≦ 17.5 30.1 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 41.2 ≦ γ < 90.0  7.5 < Al ≦ 12.5   48 ≦ γ < 90.0 12.5 < Al ≦ 17.5   44 ≦ γ < 90.0 140 < θ ≦ 144 1 < Pt ≦ 3 2.5 < Al ≦ 7.5 10.0 ≦ γ < 90.0  7.5 < Al ≦ 12.5 10.0 ≦ γ < 90.0 12.5 < Al ≦ 17.5 10.0 ≦ γ < 90.0 3 < Pt ≦ 5 2.5 < Al ≦ 7.5 26.3 ≦ γ < 90.0  7.5 < Al ≦ 12.5 19.4 ≦ γ < 90.0 12.5 < Al ≦ 17.5 18.0 ≦ γ < 90.0 5 < Pt ≦ 7 2.5 < Al ≦ 7.5   45 ≦ γ < 90.0  7.5 < Al ≦ 12.5 43.2 ≦ γ < 90.0 12.5 < Al ≦ 17.5 39.5 ≦ γ < 90.0 7 < Pt ≦ 9 2.5 < Al ≦ 7.5 48.9 ≦ γ < 90.0  7.5 < Al ≦ 12.5 48.1 ≦ γ < 90.0 12.5 < Al ≦ 17.5   48 ≦ γ < 90.0 .


13. The boundary acoustic wave device according to claim 1, wherein the piezoelectric substrate is made of LiNbO₃.
 14. The boundary acoustic wave device according to claim 13, wherein −5°≦φ≦+5°, +80°≦θ≦+130°, −10°≦φ≦+10°, and 10°≦γ<90° are satisfied, where the Euler Angles of the piezoelectric substrate are specified to be (φ, θ, φ) and the groove angle is specified to be γ.
 15. The boundary acoustic wave device according to claim 13, wherein −5°≦φ≦+5°, +200°≦θ≦+250°, −10°≦φ≦+10°, and 10°≦γ<90° are satisfied, where the Euler Angles of the piezoelectric substrate are specified to be (φ, θ, φ) and the groove angle is specified to be γ.
 16. The boundary acoustic wave device according to claim 1, wherein the groove angle is within the range of 10° or more and 80° or less. 